Catalytic carrier system



an. 30,1940, R. c. CURTIS Y 2,188,500

CATALYTIC CARRIER SYSTEM Filed Jan. 14, 1938 2 Sheets-Sheet 1INTEGRATION NETWORK .cOMPOsITE FILTER NETWORK POWER AMPLIFIER za //4 /5/6 I /7 FILTER MODULATOR:- I AMPLIFIER MODOLATION SOURCE A 'B c I oHARMoN c GENERATOR l I 2 BASE INVENTOR FRgEQUgNCY cRvc/Qa/IA C.CM/z/bi/a Q KBSOVIE'DSW ATTORNEY.

2 Sheets-Sheet 2 R. C. CURTIS CATiLYTIdCARRIER SYSTEM File d Jan. 14,1938 Jan. 30,1940.

ATEQRNEY Patented Jan. 30, 1940.

UNITED STATES CATALYTIC CARRIER SYSTEM Richard 0. Curtis, East Orange,N. L, assignor to Wired Radio, Inc.,'New York, N. Y., a corporation ofDelaware Application January 14,1938, Serial No. 184,973

11 Claims.

This invention pertains in general to signalling systems andspecifically relates to signalling systems in which modulated highfrequency energy is transmitted to a reception point with the car- 6rier frequency itself substantiallye ated but replaced at the receptionpoint for intelligibly receiving and reproducing the signal.

One object of the invention resides in providing an arrangement fortransmitting a replacement I 1 carrier frequency over a transmissionmedium,

concomitantly with the transmission of the suppressed carrier signallingenergy, the independently transmitted carrier frequency being freed ofextraneous modulation and combined 15 with the signalling energy tointelligibly reproduce the signal at the reception point. In thisconnection, the invention is an enlargement and development of thegeneral field of such systems,

as represented by the copending aplications of 20 John C. Walter, SerialNo. 84,242, filed June 9, 1936 and issued March 21, 1939 as Patent No.2,151,454; Robert D. Duncan, Jr., Serial No. 93,908, filed August 1,1936 and issued'January 18, 1938 as Patent No. 2,105,809; and Richard C.

85 Curtis, Serial No. 180,972, filed December 21, 1937. A further objectof the invention comprises providing a suppressed carrier system for thetransmission to a reception point of modulated signal high frequencyenergy with carrier sup- 80 pressed, together with an independentreplacement carrier frequency, with means at the reception point forpurifying the individually transmitted carrier frequency so that itsrecombining quality is enhanced, thereby avoiding distortion,

98 noise and other effects sometimes produced by such transmissionmethods.

A still further object of the invention comprises providing a system ofthe type indicated in which a transmitted control frequency and a 4frequency produced at the reception point are combined to effect a.catalytic function whereby any modulation that the control frequency haspicked up during transmission is removed, thus providing a clean controlfre uency for replace- 45 ment or combining purposes the reception ofsignal modulated high frequency energy with carrier suppressed.

Referring to the drawings in detail. a base frequency source 2, such asa crystalcontrolled'elec- 50 tron tube oscillator, produces a, sustainedelectric wave of a base frequency such as 10 kilocycles. This wave, orfrequency as it will be called for convenience, is delivered to aharmonic generator I which develops from the base frell quency aplurality of harmonically related higher frequencies. These higherfrequencies are discretely spaced along the frequency spectrum and arerespectively supplied to modulators 3 6 and to an amplifier I. As anexample, the frequency supplied to the modulators 3-6 may be of theorder of 30, 50, 60 and 80 kilocycles.

Modulation sources 8-H provide different signal or program frequenciescorresponding to a group of different programs to be transmitted,designated as programs A, B, C and D. These 10 modulation frequenciesare fed to the modulators 3-6 respectively, to combine with the carrierfrequencies and produce modulated high frequency ener y, the carrierfrequencies themselves being suppressed before transmission. The out- 1puts of modulators 3-6 are directed respectively through restrictingfilters l3-l6, power amplifiers |8-2l and thence to a composite filter23 and integration network 24.. The output of the integration network 24is directed through capacitive couplings to a transmission medium 25,which may be a commercial power distribution network such as used inwired radio broadcasting.

The foregoing arrangement of signal transmission is substantiallysimilar to that already dis- 25 closed in copending applications ofRichard C. Curtis, Serial No. 180,971, filed Decenfber 21, 1937 entitledStaggered frequency signal distribution; and Henry R. Butler, Serial No.161,389, filed August 28, 1937, entitled Wired radio service system, '80which issued Nov. 14, 1939 as Patent No. 2,179,612.

In the present embodiment of the invention, an amplifier 1 receives fromthe harmonic generator I a high order harmonic frequency such as 150kilocycles. This frequency is not modulated but is amplified andsupplied directly through filter l'l to power amplifier 22 and thence tocomposite filter 23 and integration network 24, to be transmitted overthe transmission medium 25 concomitantly with the transmission of theother 40 frequencies discretely located along the frequency spectrum.

In the "operation of the system, receiving equipment, positioned at areception point, includes a. wave filter 30 of the pass range typeadapted to receive substantially nothing but the 150 kilocycle frequencytransmitted over the medium 25. This transmitted 150 kilocycle wave willbe referred to as the primary control frequency to distinguish withrespect to .a second or catalytic control frequency originated at thereception point. In addition to the filter 30, another filter 3| isprovided which may have ad- .iustable parameters for selective receptionof anyone of the side bands of modulated high frell quenciescorresponding to the program channels AD which are transmitted with thecarrier frequencies substantially eliminated therefrom.

The output of filter 30 is directed to an amplifier 33 which raises theenergy level of the received primary control frequency. Theamplification characteristics of the unit 33 are adjustable so that theenergy level may be regulated. The regulated outputof the amplifier 33is directed to the input of a linear detector 33. The

detector 34 comprises an electron tube and associated circuits forproducing sum and difference detection of the input frequencies.

In accordance with the invention, a local oscillator 35 is positioned atthe, reception point for generating or producing a second control 'orcatalytic frequency. The oscillator 35 includes an electron tube andassociated circuits for generating a sustained unmodulated highfrequency wave. A crystal control arrangement may be used if desired,although in the present embodiment of my invention I prefer to use anoscillator circuit without a crystal, and adjusted to produce asustained wave of substantially 100 kilocycles. The energy level of theoutput of the oscillator 35 is controlled by adjustable control meansknown in the art, and is divided into two circuit paths 4'! and 48. Thecircuit path 41 is directed to the input circuit-of the detector 34 sothat the frequency of 100 kilocycles from osclllator 35 is combined withthe frequency of 150 kilocycles from amplifier 33 by sum and differencedetection.

In the course of transmission over lines 25, the 150 kc. controlfrequency may become modulated by devices connected to said linesbetween the transmission and reception points. Rectifying devices provetroublesome in this respect by Sum i're- Difference Input frequendeg(km) qlieklSl frequencies 160 (strong) 150.12 Eweak; 300. 12 0. 12149.88 weak 299.88 0. 12 (week) 250 50 Neither the sum nor difference oftwo weak frequencies appears in the output of a linear de-.

tectonwhen a strong frequency also is present, hence the output ofdetector 34 does not contain frequencies of 250.12 kc. or 249.88 kc. Theresult is that the beat frequencies of 250 kc. and 50 kc. are notassociated with modulation side bands and are spaced sufiiciently fromthe'other beat frequencies appearing in the detector output to be easilyselected by filtering.

The output of detector 33 is directed to a filter 35 of the pass rangetype, adjusted topass substantially nothing but the beat frequency of250 kc. This pass frequency of the'filter 35 is the For this reason, theprimary control sum of the primary control and catalytic frequenciesabove mentioned. The output of filter 36 is directed to another lineardetector 31. The detector 31 operates substantially similarly to thedetector 34 and produces sum and difference frequencies.- The circuit 48delivers the relatively weak 100 kilocycle catalytic frequency from theoscillator 35 to the input of detector 31, so as to combine with the 250kilocycles output of filter 35 in a sum and difference detectionoperation.

The output of detector 31 is directed to another wave filter 38 of thepass range type. The

filter 38 has parameters of values such that the one frequency anotherfrequency of a lower order. 25

The submultiple generator 39 produces from the frequency kilocyclesother frequencies coresponding in cycles persecond to the carrierfrequencies generated by the generator I and which were eliminated fromthe programs transmitted over the transmission medium 25. The generator39 includes adjustable circuit parameters for selectively producing adesired one of these frequencies for replacement purposes.

A desired replacement frequency from generator 39 is delivered to amixer 40 which combines the replacement carrier with the selected sideband of modulated high frequency waves delivered from filter 3|. Thecombined frequencies in the output of mixer 40 are delivered to anotherlinear detector ll and thence to a reproducing system 42 forreproduction of desired modulation as a received selected program.

In the operation of the system it is important that the energy levels ofthe outputs of amplifier 33 and oscillator 35 be adjusted so that theprimary control frequency, from filter 30, has a high energy level ascompared with the output of oscillator 35. The catalytic frequency fromoscillator 35 in the dual mixing operation in detectors 34 and 31 hasbeen found to produce a material improvement in the quality of theprimary control frequency without disturbing its harmonic relation tothe base frequency of source 2 at the transmitter. This improvement isso marked that the replacement carrier derived from the primary controlfrequency may be successfully used to reproduce the program modulationwith high fidelity and substantially without hum or noise attendant thetransmission of the primary control frequency over a power network suchas the medium 25.

The use of the word catalytic herein is analogous to the use of the wordin the field of chemistry. The catalytic frequency originated at thereception point in accordance with the invention assists in thefrequency conversion of the incoming received control frequency toremove extraneous modulation therefrom and yet, like a chemicalcatalyst, does not appear inthe end result.

Although a preferred form of the arrangement for a catalytic carriersystem has been shown, it will be recognized that various changes andmod iiications can be made by those skilled in the art I withoutdeparting from the intended scope of aisauoo the invention. Therefore,no limitation is intended except as pointed out in the appended claims.

What is claimed as new and original to be secured by Letters Patent ofthe United States is:

1. A system for selectively receiving signals in the form of suppressedcarrier side bands trans mitted over a wire network together with acontrol frequency subject to undesired modulation during transmission,said system comprising at a receiving point, means for generating asecond control frequency at low energy level compared to the first saidcontrol frequency, a linear detector for combining said first and secondcontrol frequencies to produce a beat frequency substantiallyunmodulated, means for selecting said beat frequency in the output ofsaid detector, a second linear detector for combining the second controlfrequency with the selected beat frequency to reproduce the firstcontrol frequency substantially free of said undesired modulation, meansconnected to the output of the second detector for deriving areplacement carrier from the reproduced first control frequency andmeans for combining said replacement carrier with a selected one of thereceived side bands to reproduce its signal.

2. In a receiving system having circuits controlled by a receivedcontrol frequency which is subject to undesired modulation beforereception, means for removing such modulation comprising a source ofunmodulated oscillations having a different frequency than the receivedcontrol fre quency, means including a linear detector for combining saidoscillations and control frequency, the latter strongly predominating inamplitude, to produce a beat frequency substantially unmodulated, meansfor selecting said beat frequency in the output of said detector, and asecond linear detector for combining relatively weak oscillationsfromsaid source with the selected beat frequency to reproduce thecontrol frequency substantially free of the undesired modulation.

3. A system for receiving signal modulated high frequency energy withthe carrier frequency itself substantially suppressed but accompanied bya primary control frequency, said system comprising means at a receptionpoint for originating a catalytic control frequency, a selection circuitat said reception point for receiving said primary control frequency,means for adjusting the amplitudes of said primary and catalyticfrequencies to make the former strong relative to the latter, asubstantially linear detector for combining said primary controlfrequency and said catalytic frequency, a selection circuit forselecting a resultant frequency from said combined frequencies, a secondsubstantially linear detector for combining said selected resultantfrequency with said catalytic frequency, a further selection circuit forselecting the primary control frequency from said second combinedfrequencies, means for receiving said signal modulated high frequencyenergy, and means including said selected primary control frequency forreplacing the carrier on said received signal modulated high frequencyenergy.

4. The system in accordance with claim 3 in which said last mentionedmeans includes a further substantially linear detector for combiningsaid signal modulated high frequency energy with a wave controlled bysaid selected primary control frequency in a difference detectionoperation.

5. The system in accordance with claim 3 in which said last mentionedmeans comprises a sub 6. The system in accordance with claim 3 in whichthe original canier frequency of said signal modulated high frequencyenergy, and said primary control frequency are each multipally relatedto a base frequency, and in which said selection circuits areallsubstantially adjusted to the reception of frequencies havingsubstantially multiple relationship with said base frequency.

'7. A system for removing modulation from a sustained high frequencyprimary wave which comprises, means for producing a secondary wavediffering in frequency from said primary wave, a selective amplifyingcircuit for receiving said primary wave and making it strong relative tosaid secondary wave, a substantially linear detector for combining saidprimary wave and. said secondary wave, a selection circuit for selectinga resultant wave from said combined waves, a second substantially lineardetector for combining said selected resultant wave with the relativelyweak secondary wave whereby the primary wave is reproduced withoutmodulation, and, a further selection circuit for selecting saidreproduced pri mary wave from said second combined waves.

8. In the art of transmitting and receiving a control frequency over atransmission medium the method for removing modulation acquired'by said,frequency during transmission which comprises, amplifying said controlfrequency as received, combining the same with relatively weakunmodulated oscillations of different frequency and obtaining a beatfrequency by linear detection, selecting said beat frequency andrecombining it with relatively weak oscillations of said differentfrequency to obtain by a second linear detection the said. controlfrequency substantially free of modulation.

9. The method for providing a source of unmodulated replacementca'rriers at a reception point under frequency control of a receivedcontrol wave subject to modulation during transmission, which methodcomprises generating unmodulated oscillations differing in frequencyfrom the received control wave, adjusting the relative amplitudes ofsaid oscillations and control wave so that the latter stronglypredominates, combining said oscillations and control wave by lineardetection to produce a beat frequency substantially free of modulation,recombining said beat frequency with said relatively weak oscillationsto obtain the original control wave free of modulation, and using saidunmodulated control wave as a source for frequency controlledreplacement carriers.

10. A system for removing modulation from a sustained frequency primarywave which comprises, means for producing an unmodulated secondary wavedifiering in frequency from said primary wave, means for controlling theamplitude of said primary and secondary waves to make the former strongrelative to the latter, a substantially linear detector for combiningsaid primary wave and said secondary wave, a selection circuit forselecting a resultant wave from said combined waves, a secondsubstantially linear detector for combining said selected resultant wavewith the relatively'weak secondary wave whereby the primary wave isreproduced without modulation, and a further selection circuit forselecting said reproduced primary wave from said second combined waves.

11. The method for eliminatlnz undesired modulation from a primary waveof sustained frequency which comprises mixing said primary wave at arelatively high energy level with unmodulated oscillations of differentfrequency and v a eauoo relatively low energy level, obtaining a beatfrequency by linear detection, selecting said beat frequency andrecombining it with relatively weak oscillations of said diflerentfrequency to obtain by a second linear detection said primary wave 5substantially free of said modulation.

RICHARD 0. Gimme.

